The present invention relates to a multifunctional filter and claims the priority of German patent application 103 09 428.8-23, to the contents of which reference is hereby made.
Compressed-gas, in particular compressed-air, systems require filters for separating out solid and liquid foreign substances, such as dirt particles, condensate and oil, entrained in the gas stream.
Conventional compressed-air filters generally comprise a two-part housing having a top part and a bottom part, which are either screwed together or connected to one another by means of a union nut or a bayonet fitting. The housing top part usually has an inflow passage and an outflow passage on diametrically opposite sides. The inflow passage opens out either centrally into a hollow-cylindrical filter element, which is screwed or adhesively bonded into the top part, or into the annular space between the filter element and the housing. Accordingly, the outflow passage leads either out of the annular space or out of the interior of the filter element, depending on whether the gas is to flow through the filter element from the inside outward or from, the outside inward. Consequently, the direction of flow in the filter is fixed after assembly and cannot be altered in the assembled position. The direction of flow at the same also defines the field of use of the filter; since in the case of dust filtering, the gas flows through the filter element from the outside and in the case of coalescence filtering the gas flows through the filter element from the inside in order for compressed-air condensate to be separated out. Consequently, conventional filters are only suitable for use either as a dust filter or as a coalescence filter once the direction of flow has been fixed after installation in the compressed-air system.
European laid-open specification 0 808 206 has disclosed a filter which is provided with a differential pressure indicator for monitoring the filter contamination, and this differential pressure indicator is connected to the inflow passage and the outflow passage of the filter via respective measurement passages. In filters of this type, a change in function is particularly complex since it is not only the filter which then has to be rotated through 180°, but also the differential pressure indicator, in order to return its display to the visible side.
Since liquid, in particular condensate, which is separated out in the filter collects in the bottom part of the housing and the capacity of the latter is very restricted, it is also necessary for the liquid to be discharged from time to time. This is usually done automatically under level control with the aid of a condensate discharge, wherein a level sensor in a collection space for the condensate drives a solenoid valve, which for its part actuates a diaphragm valve for opening and closing a liquid outlet in the lower part of the filter housing. As described in PCT laid-open specification WO 98/45 641, the condensate discharge may be arranged below the filter housing bottom part, which functions as a collection space for the condensate, and releases the condensate downward via an outlet passage. On account of the line connections, it is likewise no longer necessary to change the function or direction of the flow after assembly in a filter having a condensate discharge of this type.
Although a change in function is not usually necessary while the filter is operating, the drawback remains that filters provided with a differential pressure indicator and/or with a condensate discharge are in each case designed for just one direction of flow; consequently, they can be used either only as coalescence filters (direction of flow from the inside outward) or as dust filters (direction of flow from the outside inward) without being converted.